In a bit of a twist, the traditionally right-leaning Chicago Tribune editorial board has endorsed Democratic Rep. Tammy Duckworth in her bid unseat incumbent Republican Mark Kirk in the U.S. Senate.

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The Tribune Tower, home of the Chicago Tribune sits along Michigan Avenue at the Chicago River on October 8, 2015 in Chicago, Illinois. Tribune Media is reported to have hired a real estate investment banker to explore the sale of the Tower. (Photo by Scott Olson/Getty Images)

In a bit of a twist, the traditionally right-leaning Chicago Tribune editorial board has endorsed Democratic Rep. Tammy Duckworth in her bid unseat incumbent Republican Mark Kirk in the U.S. Senate.

In their endorsement, the Tribune pointed to Duckworth’s "chops for nonconformity,” crediting the congresswoman’s bipartisanship and unique perspective on military and veterans issues. Duckworth lost both legs co-piloting a Black Hawk helicopter over Iraq in 2004.

Nevertheless, the Tribune endorsed Duckworth “with the expectation that she stay focused on cost cutting as the nation navigates a debt crisis that much of official Washington recklessly ignores."

“We endorse her with the realization that Illinois already has one fierce Democratic loyalist in the Senate, Dick Durbin,” the editorial board wrote Friday. “If she’s elected, it will be Duckworth’s job to also represent the many Republican and independent Illinoisans who won’t have voted for her but who deserves a voice.”

The board also noted that Kirk’s health is a “fundamental component of this race.” The senator suffered a major stroke in 2012 that kept him out of the Senate for nearly a year. Despite the fact that his doctor said the Republican has made a “full cognitive recovery” from the stroke last month, the editorial board faulted the senator for his low-energy performance at an endorsement session earlier this month.

The Tribune also noted that Kirk is no longer “as influential an advocate in Washington as he was for more than a decade.” Before being elected to the Senate in 2010, Kirk served in the U.S. House of Representatives for nearly 10 years.

The Kirk campaign responded Friday, calling the endorsement "a low blow and cheap shot" that is "not based on fact or reality."

"The indisputable truth is that while Cong. Duckworth has been rated as one of the least effective members of Congress, Senator Mark Kirk has been one of the most successful," Kirk spokesman Kevin Artl said in a statement. "Kirk has created bi-partisan support to keep the Export-Import Bank open, saving over 40,000 Illinois jobs, he secured millions in funding for law enforcement to crack down on gang violence and he is viewed as a national leader when he bucked his own party and said he could not support Donald Trump."